Table of Content

    15 January 2017, Volume 3 Issue 1
    Key-Leakage Evaluation of Authentication in Quantum Key Distribution with Finite Resources
    2017, 3(1):  2-12. 
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    Partially information leakages of generation key undoubtedly influence the security of practical Quantum Key Distribution (QKD) system. In this paper, based on finitekey analysis and deep investigation on privacy amplification, we present a method to characternize information leakages gained by adversary in each authentication round and take the theory derived by Cederlf and Larsson into practical case. As the authentication key is fed from one round of generation keys to the next except the first round, by considering its security weakness due to information leakages and finite size effect, we further propose a universal formula for calculating the lifetime of initial authentication key used in QKD with finite resources. Numerical simulations indicate that our bound for estimating information leakages strictly characterizes the stability of practical QKD against informationleakage based attacks and our calculation formula in terms of lifetime can precisely evaluate the usage time of initial authentication key. Our work provides a practical solution for evaluating authentication security of QKD.
    Quantum Random Number Generation
    2017, 3(1):  23-35. 
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    Quantum physics can be exploited to generate true random numbers, which play important roles in many applications, especially in cryptography. Genuine randomness from the measurement of a quantum system reveals the inherent nature of quantumness—coherence, an important feature that differentiates quantum mechanics from classical physics. The generation of genuine randomness is generally considered impossible with only classical means. Based on the degree of trustworthiness on devices, quantum random number generators (QRNGs) can be grouped into three categories. The first category, practical QRNG, is built on fully trusted and calibrated devices and typically can generate randomness at a high speed by properly modeling the devices. The second category is selftesting QRNG, where verifiable randomness can be generated without trusting the actual implementation. The third category, semiselftesting QRNG, is an intermediate category which provides a tradeoff between the trustworthiness on the device and the random number generation speed.
    The Latest Developments of Fiber Quantum Teleportation
    2017, 3(1):  36-43. 
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    Since first proposed in 1993, quantum teleportation has been enjoying an enormous development both theoretically and experimentally. Quantum teleportation not only can help with investigating the foundation of quantum mechanics, but also is the footstone of quantum technologies, and it can be applied in quantum repeaters and distributed quantum computing, which are essential for a quantum network. However, before quantum teleportation can be practically applied in quantum networks, there are some technique problems that must be solved in advance experimentally, including the quantum interference between independent sources. In practical applications, quantum sources are normally separated far apart, and linked by optical fiber. To enable the interference between photons from different sources means making them indistinguishable from each other in all degrees of freedom even after they have passed through at least several kilometers of optical fiber, the properties of which can be greatly influenced by the surrounding environment. Recently, two groups (one from Hefei, one from Calgary) overcome this challenge and respectively accomplished the field test of quantum teleportation with independent sources, which marks a critical step towards the realization of a global quantum Internet.
    The Development of the ContinuousVariable Quantum Key Distribution
    2017, 3(1):  44-52. 
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    With the development of science and technology, the quantum private communication attracts attentions due to the unconditional security. As an important branch, the quantum key distribution (QKD) has developed rapidly, which has two ways: the discretevariable quantum key distribution (DVQKD) and the continuousvariable quantum key distribution (CVQKD). The CVQKD appears relatively late, but it has been developed rapidly in the past decades due to its own advantages. For CVQKD, many different protocols have been proposed, and been demonstrated from the aspect of the security. In order to verify the feasibility of these protocols, a large number of experiments have been carried out, and good achievements have been achieved, which greatly promote the development of the CVQKD technology. Base on the theory and experiments, the quantum key distribution network and its field experiment are studied. Meanwhile, the scientists have developed the prototype, which promote the applicability and the industrialization of the continuousvariable quantum secret communication technology.
    Study of Atomic Spin Entanglement in Optical Lattices
    2017, 3(1):  53-59. 
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    Multipartite entanglement is the key resource for quantum computation. Ultracold atoms in optical lattices provide a clean and tunable platform for generating scalable entangled states. We report the experimental progress on the creation and detection of atomic spin entanglement. Our experiment represents a fundamental step towards quantum computation with ultracold atoms in optical lattices.
    Measurement Device Independent Quantum Key Distribution over a 404km Optical Fiber
    2017, 3(1):  74-79. 
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    Measurement device independent quantum key distribution (MDIQKD) with the decoystate method negates security threats of both the imperfect singlephoton source and detection losses. Lengthening the distance and improving the key rate of QKD are vital issues in practical applications of QKD. Herein, we report the results of MDIQKD over 404km of ultralowloss optical fiber and 311km of standard optical fiber while employing an optimized fourintensity decoystate method. This recordbreaking implementation of the MDIQKD method not only provides a new distance record for both MDIQKD and all types of QKD systems but also, more significantly, achieves a distance that the traditional BB84 QKD would not be able to achieve with the same detection devices even with ideal singlephoton sources. This work represents a significant step toward proving and developing feasible longdistance QKD.
    Practical Technology of Quantum Communication
    2017, 3(1):  80-85. 
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    Quantum communication is the only strictly proved communication technology with unconditional security in principle. In a narrow sense, quantum communication refers to quantum key distribution, which is proved to be absolutely security based on ideal BB84 protocol. However, the idealized conditions can not be fully satisfied by real systems, wherein nonideal light sources readily get photon number splitting attack, and this security problem can be well solved by BB84 decoy state quantum key distribution.
    Research Progress of Practical Quantum Random Number Generation
    2017, 3(1):  86-90. 
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    A quantum random number generator (QRNG) is one which extracts genuine randomness from the inherent uncertainty in quantum mechanics based on a quantum system. Previous QRNGs have been implemented with the most common relying on the behavior of a photon at a beamsplitter, producing a random bit dependent on which of the two paths in which the photon is detected. It is too low for many applications. A practical highspeed quantum random number generator based on the measurement of the timing of singlephoton detection relative to an external time reference is proposed and realized. The distribution of the raw data is uniform and the raw random bit rate can reach 109Mbps. However, the rate is still not high enough for some applications such as highspeed quantum key distribution (QKD) system. A 68Gbps quantum random number generator by measuring laser phase fluctuations is implemented. The laser phase fluctuations are converted to intensity by a very stable interferometer where active feedback instead of common temperature control is developed to meet the requirement of stability. The the intensity is measured by a highspeed photodetector and then digitalized to raw data with a rate of 80Gbps. By modeling the system, the minentropy which is used to quantify the quantum randomness of the raw data can be evaluated. After Toeplitzmatrix hashing randomness extraction, the final bit rate can reach 68Gbps. However, for a practical QRNG, the speed bottleneck lies on the speed of randomness extraction, which usually is very slow. To close the gap, a pipeline extraction algorithm based on Toeplitz matrix hashing is proposed and implemented in a highspeed fieldprogrammable gate array (FPGA). Further, all the QRNG components are integrated into a compact module. The final generation rate of the QRNG module with realtime extraction and transmission can reach 3.2Gbps. The series of research progress shows that highspeed quantum random number generators are ready for practical usage.
    High-Speed Light Source for Decoy-State Quantum Key Distribution
    2017, 3(1):  91-95. 
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    A 1550nm highspeed light source is realized for decoystate quantum key distribution (QKD). Signalstate and decoystate pulses are obtained with the same pulse duration of 25ps, and similar spectral characteristics by triggering laser diode (LD) with two different electrical pulses, where the pseudorandom numbers decide which state will be generated. The same duration and similar spectral characteristics effectively avoid possible eavesdroppers attacks through temporal and spectral analysis. Meanwhile, the intensity fluctuation is controlled to meet the requirements of practical decoystate QKD with random intensity error. In addition, with the help of a highspeed singlephoton detector, the light sources characteristics are analyzed.